Hemodynamic monitoring plays an important role in managing critically ill patients in emergency departments, surgical rooms and intensive care units. Adequate blood oxygen supply to tissue is essential to sustain human life. A lasting deficiency of tissue oxygen could lead to the failure of vital organs, and is ultimately responsible for most deaths from a variety of diseases, such as trauma, burn, heart attack and sepsis. Mixed venous oxygen saturation (SvO2) is a primary target of hemodynamic monitoring. SvO2, the oxygen saturation measured from the mixed venous blood in a pulmonary artery, reflects the dynamic balance between the body's global oxygen supply and demand. Normally, SvO2 is closely maintained between 60˜80%. In patients, there are various challenges to the balance of oxygen metabolism. For example, the oxygen demand will increase in case of fever, shivering and seizure, while the oxygen supply could decrease when bleeding. When challenged, stable patients can restore the oxygen equilibrium by increasing the cardiac output, and do not require hemodynamic intervention. But, in high-risk patients, especially those with poor cardiopulmonary reserve, the compensatory increase in cardiac output is limited. As a result, bodies' last defense is called upon by extracting more oxygen from blood, that is when SvO2 starts to decrease. Immediate intervention is indicated, if a >10% deviation of SvO2 from baseline is seen to last beyond 3 minutes.
In current practice, SvO2 can be measured with an indwelling pulmonary artery catheter (PAC), introduced invasively from a peripheral vein. However, the use of PAC was found to be associated with 10% incidence of complications, including hematoma, vessel puncture and cardiac arrest. As a result, the use of PAC has decreased by about 65% between 1993˜2004. Modern echocardiography provides a clear view of the cardiac motion and a quantitative evaluation of the cardiac output. But it provides no information about the blood oxygen content.
Therefore, there is a need to address at least some of such deficiencies and/or issues, and, e.g., to provide a safe device for monitoring SvO2.